Prior Art Statement
The following patents are representative of the most relevant prior art known to the Applicants at the time of filing of the application:
______________________________________ U.S. PAT. NO. 3,406,020 October 15, 1968 W. J. D'Alessandro FOREIGN PATENT 1,207,766 October 7, 1970 United Kingdom ______________________________________
In the manufacture of resin bonded grinding wheels, a measured amount of abrasive grain is mixed with a powdered phenolic resin based bonding composition, then the resulting mix is pressed to form a wheel shape and the resin is cured. To promote a better pickup and bonding of the resin to the abrasive grains, it has been found useful to wet the grains with furfural prior to mixing the grain with the resin bond composition. The U.S. Pat. No. 3,406,020 to D'Alessandro, Oct. 15, 1968 and British Patent to Norton Company, No. 1,207,766, published Oct. 7, 1970, describe such a wheel making procedure.
D'Alessandro teaches the making of phenolic bonded abrasive wheels having various additives mixed with the grain and bond composition that are alleged to produce a bonded wheel having an enhanced flexural strength. Various kinds of abrasive grains such as alumina, corundum, silicon carbide and diamond grains are mentioned for inclusion in the wheel bonded with a novolak resin with hexamethylenetetramine hardening agent. The hardening agent is used within a range of about 2% to 50% based on the weight of the novolak, the preferred range being from about 3% to 20% and more particularly 7% to 15%. This patent describes the use of from 0 to about 100 parts of a wetting agent per hundred parts of novolak, the wetting agent being selected from a group consisting of liquid resole resin, cresol, furfural and furfural alcohol. The wetting agent is blended with the abrasive grain in proportions of about 40 parts liquid phenolic resin wetting agent to 80 parts powdered novolak binder and in another formulation of 10 to 20 parts furfural with 120 parts of solid novolak resin. The formulation is controlled so that the abrasive mix of grains, wetting agent and resin binder are free flowing at room temperature and the only criterion for determining how much wetting agent to use is that the mix should remain relatively free flowing up to the time it is charged into the mold.
The British patent is concerned with the making of an improved self-dressing manually controlled foundry snagging wheel having a resin bond, the wheel having from 22% to 26% pores by volume and the abrasive being spinel or mullite grains or mixtures of such abrasive grits. The making of wheels of such porosity is described and in the preparation of the abrasive grain and resin bond from which the wheel is molded, with reference to the use of furfural, there is only one comment and it is said that furfural is used in a conventional manner as a plasticiser in an amount of 55 cubic centimeters per pound of dry resin bond. No mention is made of the amount of hexamethylenetetramine employed.